This invention relates to a process for preparing glycol aldehyde, particularly to a process for preparing glycol aldehyde from ethylene glycol by use of a complex system catalyst comprising copper and other inorganic component.
Glycol aldehyde is a useful compound as the starting material for .alpha.-amino acids, pharmaceuticals, agricultural chemicals, chemicals for photography or special polymers, etc. and also as fiber treating agents, odorants and deodorants.
Primary known techniques for preparing glycol aldehyde from ethylene glycol are shown below.
(1) Process which comprises contacting ethylene glycol with a copper-chromium system catalyst at 300.degree. to 400.degree. C. together with hydrogen and steam (U.S.S.R. Patent No. 168281, 1965).
(2) Process which comprises contacting ethylene glycol with a copper-zinc alloy (brass) at 220.degree. to 370.degree. C. under a reduced pressure of 10 to 45 mmHg (Masato Nomura, Yoshito Fujiwara, Research Report No. 15 of Faculty of Engineering, Kinki University).
(3) Process which obtains glycol aldehyde by oxidative dehydrogenation of ethylene glycol with the use of a metal catalyst of silver, copper or gold (German OLS DE 3535483 A1).
In the above method (1), there is the problem that selectivity of glycol aldehyde is low and no glycol aldehyde can be obtained with good efficiency.
In the above method (2), the reaction system must be maintained under high reduced pressure as 10 to 45 mmHg, and moreover the liquid hourly space velocity (LHSV) must be made extremely small as 0.01/hr, whereby production efficiency is remarkably poor.
The above method (3) is a method in which glycol aldehyde is obtained by oxidative dehydrogenation as shown below by the formula (1) by using a single metal as the catalyst and introducing oxygen in an amount of 0.5 to 1.5-fold mole which is the theoretical amount or more based on ethylene glycol, but glyoxal, etc. are by-produced in large amounts and selectivity is poor. EQU HOC.sub.2 H.sub.4 OH+1/2O.sub.2 .fwdarw.HOCH.sub.2 CHO+H.sub.2 O(1)
Thus, for preparation of glycol aldehyde of high purity with good efficiency, none of the known techniques can be said to be industrially satisfactory.
Also, the process for producing glycol aldehyde from ethylene glycol by use of a copper system catalyst has a great problem of lowering in catalyst activity.